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Evaluating Effectiveness of IRS and LLIN

Insecticide treated net in Tanzania, TRAction

Research Overview

The London School of Hygiene and Tropical Medicine (LSHTM), in collaboration with NIMR and KCMC, recently completed a research study on malaria prevention methods in the Muleba district of the Kagera region in northwestern Tanzania. They investigated whether high coverage of insecticide-treated bednets (ITNs) reduced the need for indoor residual spraying of insecticides (IRS). The research aimed to determine whether the use of ITNs alone is equally effective as the combined use of IRS plus ITNs. Results from the research will provide valuable information about malaria prevention strategies and the most efficient use of resources. This information can inform decisions, such as those made by the President's Malaria Initiative and National Malaria Control Programs, about whether IRS can be phased out without sacrificing malaria control. 


Project Location

Tanzania: Muleba District
Map of muleba district Tanzania

Research Objectives

The purpose of this research was to determine the impact of implementing both IRS and universal coverage of ITNs on malaria transmission in rural Tanzania. TRAction and its research partners aimed to answer the following questions:

  • What is the Plasmodium falciparum prevalence rate in children under 14 years old in communities receiving both IRS and ITNs versus communities receiving ITNs only?
  • What is the rate of moderate/severe anemia in children under five?
  • What is the entomological inoculation rate (EIR) due to Anopheles gambiae s.l.?


Study Approach

LSHTM conducted a two arm randomized trial over the course of two years. Twenty five clusters were included in each study arm with at least 80 children per cluster.  Each cluster consisted of at least one village and was divided into a core surveillance area where surveys were conducted, and an outer buffer zone.  The study arms were:
  • Arm 1: Target groups received IRS and LLINs throughout both the first and second years of the study.
  • Arm 2: Target groups received IRS and LLINs during the first year of the study. During the second year of the study, IRS was withdrawn so that groups in this arm received only LLINs during year two.

Three post-intervention cross-sectional household surveys were undertaken in 2012. For each survey 80 households were randomly selected in the core area of each cluster. Households were eligible for the study if they had children aged 0.5-14 years. Any child aged 0.5-14 years was eligible to be included in the study. Up to three children per household were randomly selected for testing. Selected children were tested on the following day for malaria parasites using rapid diagnostic tests.


Key Findings

At baseline malaria prevalence, anaemia, ITN ownership, ITN usage and mean EIR per month were similar in the two study arms. After the intervention, the malaria prevalence was lower in the ITN+IRS arm than in the ITN only arm in all three surveys. Prevalence of moderate to severe anaemia in children under five years old was lower in the ITN+IRS arm in all post intervention surveys, but the difference was only statistically significant in survey B. Mean haemoglobin was lower in children under five years old in the ITN+IRS arm than in the ITN only arm in all three surveys. For all surveys, as per-protocol analysis showed statistically significant evidence for a protective effect of the combined intervention on malaria prevalence.


Lessons Learned

This is the first trial to provide evidence that IRS, when used in combination with ITNs, can give significant added protection against malarial infection compared to ITN use alone. There was also some evidence that anaemia prevalence was lower in communities with the combination. Exposure to infectious mosquito bites was about one sixth in communities with the combined intervention compared to those in the ITN only arm. National Malaria Control Programs should consider implementing IRS in combination with ITNs if local ITN strategies alone are insufficiently effective and cannot be improved. Given the inconsistent trial evidence, it would be prudent for malaria control programs implementing the two methods simultaneously to monitor the impact of the combination in relation to LLINs alone.


Research Into Action

The results of this research were shared with local and national Ministry of Health partners as well as NGOs involved in malaria control.  Additional dissemination events occurred at international public health conferences including the American Society for Tropical Medicine and Hygiene (ASTMH) conference.


Research Partners

Principal Investigator: Mark Rowland
National Institute for Medical Research (NIMR), Tanzania
Kilimanjaro Christian Medical College (KCMC), Tanzania

Project Status

Country / Countries: